Cracked naphtha desulfurization



April 28, 1953 R. c. ARNOLD ETAL 2,636,843

CRACKED NAPHTHA DESULFURIZATION Filed Oct. 9, 1950 CAT. CRACKEDNAPHTHA.279%S TOPPING 25% OvERI-IEAD .I5%s

(DIsT-I BOILING BELOW 270'F.

75% BOTTOMS'.3l5%S I BOILING ABOvE 270F.

ACID TREAT E IOI5 /BBL 2.7% (2.0%) SLUDGE I H2804 9OIOO%, 98%

3* 97.3% (73.0%) TREATED OIL RERuN 94.7% (69%) OvERHEAD.O?e%s (.DIST.)BOILING BELOW 395E 5.3% (4%) BOTTOMS- 3.3%s

HYDRODESULFURIZE SULFACTIVE CAT.

700 --950 F. H28 2oOI5OO I=. s.I.

.sI5 V/HR/V 1 H2 PRESENT 92% (3.6%) LIQ. PROD- .75%s

FRACTI ONATE 32% (I.9%I OVERHEAD .2e%s

(DIsTI I I LINE 48%(I.T%I BOTTOMS I.3%s g s (FURNACE OIL) I INvENTORs;

ROBERT C. ARNOLD ARTHUR B. LIEN JOHN F. TERs BY: M A *BASED ON ORIG.CHG.

ATTORNEY:

Patented Apr. 28, 1953 ascetic I caaonnn NAPHTHA DESULFURIZATIUN RobertC. Arnold, Park Forest, 111., Arthur 1?. Lien, Highland, and John F.Deters, Valparaiso, ind, assignors to Standard Oil Company, Chicago,l[ll., a corporation of Indiana Application October 9, 1950, Serial No.189g154 5 (Claims. 1

This invention relates to the desulfurization of cracked naphthas and itpertains more particularly to an improved combination process forrefining a relatively wide boiling range cracked naphtha which ischaracterized by a high olefin content.

Various processes have been proposed for the desulfurization of crackednaphthas of the gasoline boiling range, but heretofore such processeshave always been subject to severe disadvantages. Acid treating suchnaphthas results in undesirable olefin polymerization and/or suchreactions as alkylation, condensation, etc., and it has heretoforeresulted in relatively large losses to sludge. Solvent extractionprocesses result in removal of olefins and aromatics as well as sulfurcompounds, create an extract disposal problem and usually arecharacterized by undesirably low yields and often by loss in octanenumber. I-Iydrodesulfurization (i. e. hydroforming, hydrofining, etc.)effects lowering of sulfur contents with only small treating losses butrequires very expensive equipment as well as high operating costs;furthermore, hydrodesulfurization processes are subject to disability ofeffecting olefin saturation which not only consumes valuable hydrogenbut lowers the octane number value of the resulting product. The objectof our invention is to provide a relatively inexpensive process Whichwill avoid the objectionable features of prior art processes and whichwill at the same time result in the production of maximum yields of lowsulfur gasoline without impairing octane number.

A further object is to provide an improved topping-acid treating-toppingprocess which will minimize treating losses, maximize yields and producea product which meets strict sulfur specifications without sufferingappreciable octane number loss. An important object is to alter thechemical composition of the sulfur compounds in the acid treating stepso that most of the sulfur compounds can be removed from acid treatedoil in a simple distillation (topping) or rerun step and concentrated ina bottoms fraction which constitutes only about 5% of the initialcracked naphtha and which provides a unique and advantageous chargingstock for hydrodesulfurization by processes such as hydroforming orhydrofining. Still another object is to convert these rerun bottoms formarkedly increasing the ultimate yield of desulfurized gasoline and forproducing a by-product suitable for use as furnace oil. Other objectswill be apparent as the detailed description of the invention proceeds.

Our invention is particularly applicable to the desulfurization ofcatalytically cracked naphthas but it .is also applicable to thermallycracked naphthas, such, for example, as coke still naphtha, which is oneof the most difficult to desulfurize. We first subject the high sulfurcracked naphtha charging stock to a topping distillation step and takeoverhead components boiling below about 250 to 300 F., the preferred cutpoint being at 270 F.; we have found that the overhead fraction from thetopping step is particular- 1y rich in olefins but contains less thanhalf the amount of sulfur that is contained in an equivalent amount ofthe higher boiling bottoms from the topping step.

Next we acid treat the bottoms from the topping step, preferablyemploying about to pounds per barrel of a strong acid, such as 90 to100%, e. g. 98%, sulfuric acid. The acid treating is preferably at acontrolled low temperature in the range of about to F., althoughadvantageous results are obtainable with treating temperatures as highas to F. The sludge loss in such an operation amounts only to about 1 to3% based on the initial cracked naphtha,

this loss being minimized by the absence of olefins and other lowboiling components removed in the initial topping step. The acid treatedoil may be neutralized and/or water washed, in the conventional manner,and this oil (which constitutes about "73% of the original chargingstock) is rerun in a second topping step to take overhead all gasolineboiling range components and leave as bottoms only components which arehigher boiling than gasoline. The overhead from this rerunning step mayconstitute about 69 or 70% of the original charging stock and it ischaracterized by a sulfur content of only about 07% so that when it isblended with the overhead from the first topping step a 94: weight percent yield of gasoline is obtainable with a sulfur content of less than.1% and with an octane number which is substantially the same as that ofthe original charging stock.

The bottoms from the rerun or second topping step may amount to about 4to 5% of the original charging stock and may contain 3 to 4% of sulfur.Such bottoms are Very different in chemical composition from extractsobtained by use of selective solvents since the nature of the sulfurcompounds has been radically changed in the acid treating step. Thesererun bottoms are subjected to hydrodesulfurization, for example, tohydrofining by contact with cobalt-molybdatecan-alumina catalyst at apressure of about 1500 p. s. i. in the presence of added hydrogen. We

components.

find that the products produced are not of the same approximate boilingrange as the charge to the hydrofining step (which is usually the casein hydrofining operations) but on the contrary contains about 52% ofcomponents boiling in the gasoline boiling range and containing onlyabout 26% sulfur. By subjecting only about 4 or 5% of the originalcharging stock to hydrofining conditions, which can be done in verysmall equipment and with only a small amount of added hydrogen, we canobtain about a 2% increase in gasoline production and at the same timeobtain a valuable by-product oil. Thus, by our unique combination oftreating steps we are able to obtain from cracked naphthas containing.2% to 3% sulfur a finished gasoline containing less than .1% sulfur andwith substantially no change in octane number. We are able to obtainyields of about 96 weight per cent (even greater on a volume basis)along with a valuable by-product oil and weare able to obtain thisphenomenal result in relatively inexpensive equipment and at low costsince the volume of the hydrodesulfurization charge is only about 5% ofthe volume of the initial high sulfur cracked naphtha.

The invention will be more clearly understood from the followingdetailed description of specific examples read in conjunction with theaccompanying drawing, which is a schematic flow diagram illustrating ourimproved sequence of steps.

Referring first to the process illustrated in the drawing, we willdescribe results obtained by treating a high sulfur, stabilized,catalytically cracked naphtha having an initial boiling point in therange of 150 to 175 F. and an end point of approximately 400 F., saidnaphtha having a sulfur content of 279% by weight. We first top thischarge stock by distillation in any conventional manner to remove anoverhead stream containing components boiling below 270 F.; in. thiscase the overhead stream constituted about 25% of the initial charge,was

'highly olefinic and contained only about sulfur. It is important thatthe cut point in this initial topping operation be in the range of about250 to about 300 F. and for,most stabilized cracked naphthas, atoppingat this out point gives an overhead amounting to about to 50% of theinitial charge, best resultsbeing obtainable with a cut point ofapproximately .perature in the range of about 40 to 100 F..

preferably in the range of 40 to 60 F., followed by the conventionalsludge separation, water washing and neutralization steps, there was aloss of hydrocarbon in the acid sludge corresponding to 2.7% by weightbased on the charge to the acid treating step (2% by weight based oninitial charge). This acid treated stream is then rerun in a secondtopping distillation step to remove overhead all gasoline boiling rangeThe cut point will depend on particular gasoline specifications and isusually approximately 400 F., but in this example the cut point was at395 F. and the overhead stream, which constituted 94.7% of the materialcharged to the rerun step or about 69% of the initial charge, wascharacterized by a sulfur content of only 076%. When this stream wasblended with the overhead stream from the first topping step, a 94weight per cent gasoline yield was obtained and the product wascharacterized by a sulfur content of only 094%, its clear and leadedoctane numbers being substantially the same as those of the originalcharging stock. While the yield and quality of gasoline thus farproduced are remarkably good, we have discovered that the ultimategasoline yield can be still further enhanced by further treatment of thebottoms from the rerun steps which constitute about 5.3% of the materialcharged to the rerun step or 4% of the initial charge and which ischaracterized by a sulfur content of about 3.3%, a refractive index m of1.5105 and a density of 0.926.

When this relatively small quantity of rerun bottoms was subjected toconventional hydrofining conditions, i. e. contacted with acobaltmolybdate-on-alumina catalyst at a temperature in the range of700-800 F., at a pressure in the range of 1300-1500 p. s. i., in thepresence of added hydrogen with a reaction time of about 4 hours (testconditions to duplicate as closely as possible results that would beobtained in a commercial hydrofining operation), we obtained a 92 volumeper cent yield of a liquid product stream which contained only 375%sulfur, had a refractive index (11 of 1.4800 and a density of 0.345.This product stream constituted in this case 3.6% by weight of the totalstock charged to the first topping operation. When the liquid streamfrom the hydrofining step was distilled, it was found that 52% of thisstream constituted components in the gasoline boiling range, had aninitial of 95 F., a 50% point of 266 F. and an end point of 401 F.

This gasoline material was characterized by a sulfur content of only26%, a refractive index (72, of 1.3990 and a density of 0.778. Ordinarycharging stocks which are subjected to hydrofining conditions are notmaterially a1- tered in boiling range during the hydrofining step, butin this case more than half of the stantially the same as that of theinitial high sulfur cracked naphtha. In addition to this remarkablegasoline yield, we obtain as bottoms from the last distillation step anoil which contains less than about 1.3% sulfur and which can thus beemployed as a valuable component in furnace oils or other marketableproducts.

The hydrodesulfurization step when applied to the acid treating rerunbottoms gives results which are entirely and radically different fromresults obtainable when ordinary solvent extraction extracts aresubjected to hydrodesulfurization because such extracts do not give amarked change in product boiling range. In the specific examplehereinabove described, the hydrodesulfurization was effected with cobaltmolybdate catalyst, but it should be understood that it may be effectedby use of other known hydrofining or hydroforming catalysts such asmolybdena on aaluminacoraother nth. roup metaloxides or sul- .fides on,alumina either'ralone' or ino njlm tlfl with-an oxide-orssulfide.of-znickel :or: cobalt. This class of catalysts is commonlyknown in. art

asflsulf active hymcgenation (or dehydrogenation) catalysts. alystscobalt molubclate or nickel tungstate (suppontedand: in the. form ofsulfides :as well as For hydrofining with such-oatoxides'),theltreatment is preferably at a tempera.- tureiinthe range :of: about650 110 .809" unclera pressure in the range of about 260 to 2000 p. s.i., usually. 1500 to 1580 p. s. i., with a space velocity oftheiorder.of .2 to l5,,e. g. about :5 volumes of liuuidpharging.stockper' hourvolume-of cat-- alyst; with a gas recyclerate ofcaboutrlmlo to 5900 7the gas recycle rate being substantially the same in both cases and thepressure being in the range of'ZOU to 500p. s. i. It should beunderstood, of course, that by using increased amounts of hydrogen andincreasing the. severity of the treatment, the desul'fur'ization may beto a much greater extent than set forth in the above described example.

While in the example hereinabove described we employed catalyticallycracked high sulfur naphtha having a sulfur content of approximately 3%,the invention is also applicable to thermally cracked naphtha such asthe coke still naphtha which is produced by thermally cracking highsulfur gas oil and/or reduced crude, at a temperature of about 900 to950 under a pressure of about atmospheric to 109 p. s. i. with suchholding time that solid coke is formed. The naphtha fraction of theoverhead stream from a coking operation may have a sulfur content ofabout .6 to 37%. When such a coke still naphtha is topped to about 25%,the overhead stream in one run was found to contain 28% sulfur while thebottoms contained 379% sulfur. When these bottoms were treated with 98%sulfuric acid (12 pounds per barrel), a treating loss to sludge of 2.3%was obtained and the acid treated oil before rerunning had a sulfurcontent of 58%. The overhead from the rerunning step had a sulfurcontent of while the bottoms from the rerunning step had a sulfurcontent of 3.2%. The rerun bottoms in this case may be hydrodesulfurizedas hereinabove described to augment the total gasoline recovery. In thecase of coke still naphtha, the desulfurization is not nearly ascomplete as it is in the case of catalytically cracked naphtha and theresulting product does not meet strict sulfur specifications. While ourinvention may thus be advantageously employed with coke still naphtha,it will be apparent that coke still naphtha is by no means theequivalent of catalytically cracked naphtha in our process and for bestresults our process should be employed for the desulfurization ofcatalytically cracked naphtha.

In the acid treating step, we prefer to employ sulfuric acid at about 90to 1.00% acid strength, preferably about 98%. The amount of acid shouldbe of the order of about to 15 pounds of acid per barrel of initialbottoms charged to the :acid. treating: step. Sludger'losses are:minimized in. the. acidi treatingrbyr holding: the.;treatingtemperature.intherange; of; aboutzeorto 56.05" While sulfuric acidgives: excellent results. it should. be: understood that. other. strong"acids, suchas hydrogen fluoride-may: be employed under conditions toactually react witlncomponents of the charge. and to effectthe'conuersion' of at leastabout3 to 5% zofithecharge:intornaterialshigher. boiling than. gasoline. .Such. materials serve as. a chargingstoiclrifor. our hydrodesulfurization step.

lnanother. example ofpur inventicniasapplied to. a; high sulfurcatalytically' cracked. naphtha,

of which the initial cut point in the first toppin step was. 270.? 7.5%.bottoms. from the first topping step. (boilin in. the range. of 270 to395 F.) weretreated. with. 12 pounds of 98% sulfuricacid at atemperature ofiabout. 5'5 and the acid treated oil was rerun to produce395F. end point gasoline. In this case, we. obtained inthe rerunningstep a gasoline yield of 94 weight vper....cent of the. materialscharged to said acid treating anda. desulfurization of. 81% basedon saidmaterial. Basedon total cracked napht the gasoline yieldpriorto'thefinal hydrodesulfurization step was 95.5 weight per cent of a gasolinecontaining only 118%. sulfur, the sludge loss in this case being only1.8 weight per cent and the rerun bottoms being about 2.7 weight percent based on initial charge. By hydro'desulfurization of the rerunbottoms, it willbe seen that the total gasoline yield can be oftheorder' of 97%, the gasoline containing less than .l% sulfur and withsubstantially the same octane number as the original catalytioallycracked naphtha. In addition to this remarkably high yield of highquality gasoline, we obtain a by-product oil which serves as a valuablecomponent in furnace oil or the like.

From the above examples, it will be seen that we have accomplished theobjects of our invention. We have increased the amount ofdesulfurization accomplished per unit amount of acid used, loweredgasoline losses to sludge, augmented gasoline yields by thehydrodesulfurization of rerun bottoms and obtained about 95 to 97%yields of high quality gasoline which meets strict sulfur requirements,i. e. contains less than .1% sulfur. Only a very small amount ofmaterial requires treatment by hydrodesulfurization and this material isinitially all higher boiling than gasoline but is converted chiefly intogasoline boiling range hydrocarbons. Saturation of olefins is minimizedin the acid treating step and is nil in the hydrodesuifurization step.The high octane number of the charging stock is not materially altered.

We claim:

1. A process for desulfurizing a high sulfur catalytically crackednaphtha which process comprises topping said cracked naphtha at a cutpoint in the range of 256' to 300 F. to obtain a first overhead streamwh ch is rich in olefins and low in sulfur content, acid treating thebottoms from the topping step with the equivalent of about 98% sulfuricacid employed in amounts of 10 to 15 pounds per barrel, at a temperaturein the range of ll) to 100 F. to form about 1 to 3% of sludge and anacid treated oil containing com ponents higher boiling than gasoline,rerunning said acid treated oil. to separate gasoline boiling rangecomponents from higher boiling range components, hydrodesulfurizing saidhigher boilin range components to produce additional amounts of gasolineboiling range components and blending said additional amounts of saidgasoline boiling range components with gasoline boiling range componentsfrom the rerunning step and with low boiling components from the toppingstep to obtain a finished gasoline of low sulfur content.

2. The method of claim 1 wherein the hydrodesulfurization step iseffected by contacting the higher boiling range components from thererunning step with a sulf-active hydrogenation catalyst at atemperature in the range of I to 950 F., under a pressure in the rangeof 200 to 1500 p. s. i. and in the presence of added hydrogen.

3. The method of desulfurizing a cracked naphtha boiling chiefly in therange of about 150 to 400 F. and containing at least about .2% sulfur,which method comprises topping said cracked naphtha to remove as a firstoverhead stream components lower boiling than about 270 F., acidtreating the bottoms from the topping step with sulfuric acid underconditions for effecting substantial desulfurization and the productionof components boiling above 400 F., separating sludge formed in the acidtreating step, rerunning the acid treated naphtha to obtain a secondoverhead stream consisting essentially of gasoline boiling rangecomponents and higher boiling oil formed in the acid treating step,hydrodesulfurizing said higher boiling oil to produce additional amountsof gasoline boiling range components and blending said last namedcomponents with gasoline boiling range components contained in saidfirst overhead stream and gasoline boiling range components in saidsecond overhead stream to obtain a finished gasoline of low sulfurcontent.

4. The method of claim 3 wherein said hydrodesulfurizing is efiectedwith an alumina-supported cobalt molybdate catalyst at a temperature inthe range of about 700 to 800 F. under a pressure in the range of about700 to 1500 p. s. i. and a space velocity in the range of about 2 to 15.

5. The method of claim 3 wherein hydrodesulfurizing is effected with analumina-supported molybdenum oxide catalyst at a temperature in therange of 800 to 950 F., a pressure in the range of 200 to 500 p. s. i.and a space velocity in the range of .5 to 2.

ROBERT C. ARNOLD. ARTHUR P. LIEN. JOHN F. DETERS.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,881,534 Harding Oct. 11, 1932 2,070,295 Morrell Feb. 9, 19372,219,109 McCormick Oct. 22, 1940 2,255,394 Schulze Sept. 9, 19412,487,466 Nahin Nov. 8, 1949 2,574 Porter et a1 Nov. 6, 1951 FOREIGNPATENTS Number Country Date 345,738 Great Britain Apr. 2, 1931

3. THE METHOD OF DESULFURIZING A CRACKED NAPHTHA BOILING CHIEFLY IN THERANGE OF ABOUT 150 TO 400*F. AND CONTAINING AT LEAST ABOUT .2% SULFUR,WHICH METHOD COMPRISES TOPPING SAID CRACKED NAPHTHA TO REMOVE AS A FIRSTOVERHEAD STREAM COMPONENTS LOWER BOILING THAN ABOUT 270*F., ACIDTREATING THE BOTTOMS FROM THE TOPPING STEP WITH SULFURIC ACID UNDERCONDITIONS FOR EFFECTING SUBSTANTIAL DESULFURIZATION AND THE PRODUCTIONOF COMPONENTS BOILING ABOVE 400*F., SEPARATING SLUDGE FORMED IN THE ACIDTREATING STEP, RERUNNING THE ACID TREATED NAPHTHA TO OBTAIN A SECONDOVERHEAD STREAM CONSISTING ESSENTIALLY OF GASOLINE BOILING RANGECOMPONENTS AND HIGHER BOILING OIL FORMED IN THE ACID TREATING STEP,HYDRODESULFURIZING SAID HIGHER BOILING OIL